Generally, it is known to spray paint or coat articles by an apparatus which uses one or more spray guns mounted on a housing which defines a spray chamber. The spray guns include nozzles which extend into the chamber for spraying a coating composition onto the articles. In some applications, it is desirable or necessary to heat the coating composition before it reaches the spray guns in order to effect proper spraying through the nozzles. Typically, the coating composition is heated at a location removed from the coating apparatus or, at least, the housing of the apparatus.
An example of an application where the coating composition must be heated is when using ultraviolet (UV) curable coating compositions. A 100% solids UV curable composition is a liquid composition and is void of solvents or dilutents which must be driven off in a curing or drying process. A UV composition cures only when exposed to ultraviolet light. A UV curable coating composition or material must be heated by the time the material reaches the spray gun of the coating apparatus.
Problems are encountered in using coating compositions which must be heated for spray coating purposes. Typically, the coating composition or material is heated at the source or supply thereof, i.e., before it teaches the spray guns at the coating apparatus. During transit, even with small distances, the coating material has a tendency to cool down before it reaches the spray guns. Another problem is maintaining consistency of the sprayed material. This is particularly a problem with “atomization” type spraying nozzles whether using UV compositions or other atomizing spray material. Different temperatures can cause different atomization characteristics, and the different temperatures can be caused simply by changes in the temperature of the environment surrounding the coating apparatus, much less differences in temperatures caused during transit of the coating material to the spray guns.
Still another problem with spray coating apparatus as described above, even divorced from the stated temperature problems, is the problem of dripping caused by the spray material forming droplets at or near the end of the nozzles of the spray guns. If a droplet of spray material falls on the article to be sprayed, a blemish is created. The present invention not only is directed to solving the problems associated with inconsistent temperatures at a spray gun, but the solution to those problems also functions to eliminate material dripping from the nozzles of the spray guns.